Underground electric conductor.



No. 7|I,4|4. Patentsd Oct. I4, |902.

C. BOREL. UNDERGROUND ELECTRIC CONDUCTOR.

(Application Bled June 11, 1902.)v

(No Iodel.)

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UNITED STATES PATENT OFFICE.

CHARLES BOREL, OF L YONS, FRANCE, ASSIGNOR TO SOCIT FRANCAISE DES CBLESELECTRIQUES, (SYSTME BERTHOUD, BOREL ET CIE.,) OF

LYONS, FRANCE.

UNDERGROUND ELECTRIC CONDUCTOR.

SPECIFICATION forming* part f Letters Patent NO. 711,414, dated October14, 1902.

Application led June 11,1902. Seria-11%. 111,135. (No model.)

To all whom, it may concern:

Be it known that I, CHARLES BOREL, a citizen of the French Republic,residing at Lyons, France, have invented certain new and usefulImprovements in Underground Electric Conductors, of which the followingis a speciiication. l

This invention relates to conduct-ors of electric currents which are tobe placed underlo ground, and particularly to cables.

The excessive rises of voltage which occur in underground electricconductors in consequence of sudden disturbances in the conditions ofthe circuit are now well known. The

x5 remarkable works which C. P. Steinmetz has published on the subjectsupply a complete analysis of these phenomena and determine theconditions under which they are produced with the greatest intensity.These exzo cessive rises of voltage are sometimes such that on opening ashort circuit no insulator can efficiently resist them. Steinmetz citesan example in which the great rise of voltage resulting from the suddenopening of a short z 5 circuit amounted to three hundred and thirtythousand volts, while the normal voltage of the system was only tenthousand volts. It is therefore necessary that if it be desired to haveunderground cables which can in all 3o cases withstand the accidentalexcess in rises of voltage referred to by Steinmetz they should beconstructed with such thickness of insulator that their cost would beexcessive, rendering their use unattainable. I have 3 5 thereforeendeavored to remedy this evil and in studyingr the matter very closelyhave found the following solution: It does not consist in constructingcables with remarkable material having electric resistance ten timesthat 4o ofknown materials, but in constructing cables with insulatingmaterials usually emp1oyed,introducing, however,an arrangement whichconstitutes my invention and which is based on the well-established lawwhich prevents the occurence of oscillations of voltage in any possiblecase. Steinmetz has ascertained and demonstrated that these excessiverises of voltage, dangerous for electric cables, come, in fact, from thecables themselves. Theyarecausedbyoscillatingcharges 5o and dischargesof the condensers which are formed by the conductors andprotecting-coverings of the cables, and it is proved that thesephenomena cease to be oscillatory and are transformed into a logarithmiccharge when the resistance of the circuit is greater than twice thesquare root of the inductance by the capacity of the line, or, in otherwords, the square root of the quotient of the self-induction divided bythe capacity of the line 6o UIQVROMJIZM, C

In order, therefore, to diminish excessive rises of voltage by suddenvariations of conditionsin a system, it is necessary to increase theresistance-of the conductors in the system and to introduce a resistancein the circuit in such a manner that the relation above stated shall besatisied; but under these con- 7o ditions the loss in conductivity wouldimmediately be very great and the working would be far from economical.Here I would observe that it is necessary to oppose this resistance onlyto the charge and discharge cur- 7 5 rents of the conductor of the cableand not to the usual operating-currents. In order that this may bedone-that is to say, in order that the resistance of the circuit may beincreased only for the charge and discharge 8o currents of theconductors without affecting the operating-currents-I have devised aconstruction of the conductors of the cables iu the following manner:Around each conductor of a cable I put a conducting-cover,concentrically surrounding the whole of it, the cover being insulatedfrom the conductor itself by a thin concentric layer of insulatingmaterial.

In the accompanying drawings, which illus- 9o trate embodiments of myinvention, Figure l is a transverse section, and Fig. 2 a longitudinalsection, of a cable having two parallel conductors. Fig. 3 is a sideelevation of the cable represented somewhat diagrammat- 9 5 ically. Fig.4 is a cross-section of a cable with three conductors of twisted wireswith wire covers. Fig. 5 shows the conductor pro-v vided with a coverformedof insulated wires. Fig. 6 is a diagrammatic view illustrating acable with two conductors having Wires of high resistance woundhelically about them. Fig. 7 illustrates a modification of theconstruction seen iu Fig. 6.

Referring primarily to Figs. l and 2, C and C are two parallelconductors, each of which is surrounded by a concentric conductingcoverE and E', insulated fromthe conductor by an insulating layer 1.'. Eachconductor thus surrounded by its cover is then insulated in the usualway from its neighbor and from earth by the insulating material I. Ifnow at one of the ends of the cable-for instance, at thegenerating-station-we connect the conductor C to its cover E by a wiref', the charge-currents of the conductor C will all pass to the cover E,since it everywhere surrounds it and really constitutes its externalsurface, and it is proved that static electricity passes always to thesurface of conductors. As the cover E is insulated throughout its lengthfrom the conductor C, except at the end where it is connected by thewire f', all the charge and discharge currents of the conductor willtherefore pass by this wire to the surface of the cover, while theoperating-currents will continue to pass by the conductor C. For theconductor C it is the same when the cover E, which everywhere surroundsthe conductor C', is connected to this conductor by a wire f2. It iseasy to make the wires f f2 joining the covers to the conductors ot'suflicient resistanceto prevent the discharge of the condensers formedby the covers E and E from being oscillatory. This resistance whichthose wires must have may be easily calculated by the relation which hasbeen stated above. I haveindicated them on the drawings by the letter r.

If in a system of underground cables of great extent the capacity of theconductors is great and if owing to this the charge and dischargecurrents should have great tension, it will be necessary when sucha'system is to be constructed with my cables having their conductorsdivided into two, the one `for the operating and the other for thecharge currents, vto connect only at the generating-station the outerconducting layer to the conductor, properly so called, by a wire ofsuitable resistance; but these outer conductingcovers maybe made inseveral independent sections, each connected for itself by a wire of thedesired resistance to the central conductor. This division of conductinglayers for charge-currents and the connection of a section to thecentral conductor may be effected in the kiosks or the connecting-boxesof the system. Fig. 3 is a diagram of a long line of cable with twoparallel conductors, each divided into two, according to my system,showing the way in which the conducting-cover can be divided intosections each separately connected to the central conductor. Theinsulating layer 1I, which separates the concentric conducting-cover Efrom the conductor proper, C, and this conductor, may be made as weak ascan possibly be made. The conducting-cover E may be a thin lead tube puton by hydraulic pressure, like the protecting lead covers which usuallysurround cables. This cover E may also consist of a tin, zinc, or otherconducting-ribbon wound helically over the insulating layer z'. It mayalso consist of a concentric circle of cylindrical wires, of copper orother conductor, wound on the insulating layer t'. This cover E thenresembles the external conductor of cables made with two concentricconductors. Fig. 4 is a section of a cable having three twistedconductors provided with my covers E for charge-currents, each coverconsisting of conducting-wires arranged in a concentric circle. Thecover E for charge-currents may also consist of separately-insulatedwires fr, twined directly on the central conductor C without irstputting an insulating layer on this conductor. This circle of peripheralinsulated wires around the conductor C is the same as that which is theobject of the French patent, No. 27 7,979; but instead of beingconnected to the two ends of the cable, so that it conducts at the sametime the operating and the charge and discharge currents, this cover isnow (in order to obtain the result herein explained, which hasoccasioned my present invention) connected only by one of its ends tothe central conductor, not directly, but through a suitable resistancesufficient to render the discharges from this circumferent-ial layer ofwires not oscillatory.

Fig. 5 shows a conductor C, furnished with a concentric cover ofinsulated wires w, connected at one end only to the central conductor bya conducting resistance-wire r. By means of this concentric cover forcharge and discharge currents, formed of insulated circumferentialwires, the auxiliary resistancewires r, connecting the central conductorto the circumferential cover at one of its ends, may be dispensed with,which has the great advantage of simplifying the distributingarrangement and the connecting-boxes, these apparatus being generallyovercharged. In order to attain this result, it suices to make theconcentric exterior conductingcover consist of a small number ofinsulated circumferential wires, such as two or three, or even ko asingle insulated wire, the wire or wires being wound around the centralconductor in a helix of very short pitch. The wire or 4wires wou ndhelically may be of material 'of relatively high specific resistance,such as lead, ferro-nickel, German silver, &c. Then in order that at allparts of the conductor the charges and discharges of the circumferentialwires may pass through the desired resistance r they must be connecteddirectly to the centralv conductor, not at the same end for all theconductors of one cable, but for a cable having two twistedconductors-for instance, as shown diagrammatically in Fig.

IIO

6. The wire which helcally surrounds the conductor C is directlyconnected to it at the end next the generating-station, (the right inFig. 6,) and the wire surrounding the conductor C' is connected to it atthe end next the system, (the left in Fig. 6.) In this way the chargeand discharge currents of two points m and n, facing each other at, say,one-third of the length of the cable, must pass for the circumferentialwire of C first through one-third of its total length, then that of theconductor C two-thirds of this wire, making up together the total lengthof the wire Wound on the conductor. If, therefore, one of thesehelically-wound wires has in the rst instance a resistance 0" sufcientfor preventing the discharges of the capacity of the cable from beingoscillatory, it is no longer necessary to connect it to the centralconductor by an auxiliary resistance, but it can be connected directly.'For cables having three conductors the connections of the helical Wiresof high resistance to their respective conductors are situated inquincunX arrangement, as shown diagrammatically in Fig. 7.

The section of the insulated wires constituting my covers for charge anddischarge currents may be of any shape-cylindrical, square, rectangular,&c.

Having thus described the nature of this invention and the best means Iknow for carrying the same into practical effect, I claiml. Anunderground electrical conductor having a conducting-cover of tubularform over the whole of it, disposed concentrically with it and insulatedfrom it throughout its length, said exterior and interior conductorsbeing electrically connected at one end by a conductor of suitableresistance, substantially as lset forth.

2. An underground cable having parallel electric conductors each havingan inclosin-g conductor of substantially tubular form disposedconcentrically with the inner conductor and insulated from it by a thinlayer of insulating material, the said outer and inner conductors beingconnected at their ends by a metal conductor of suitable resistance andall the conductors of the cable embedded in an insulating material,substantially as set forth.

3. An underground electric conductor comprising an inner conductorhaving an outer conducting-covering composed of helically- Woundinsulated wire, the said inner conductor being connected at one end onlywith the wire or wires forming the outer conductingcovering,substantially as set forth.

In witness whereof I have hereunto signed my name in the presence ot'two subscribing witnesses.

CHARLES BOREL.

Vitnesses:

EUG. DUMONT, LoUIs DNRAZ.

